[PATCH] drm/amdkfd: support file backed SVM range

[Philip Yang]

HMM migrate helper migrate_vma_pages do not migrate file backed pages to
replace it with device pages because the pages are used by file cache.
We can not migrate the file backed range to VRAM, otherwise CPU access
range will not trigger page fault to migrate updated data from VRAM back
to system memory.

For file backed range, don't prefetch migrate range to VRAM, always map
system pages to GPU and also use system pages to recover GPU retry
fault.

Add helper to check if range is file backed or anonymous mapping.

Signed-off-by: Philip Yang <Philip.Yang at amd.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 40 ++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index f811a3a24cd2..69237d2ab2ad 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -2400,6 +2400,36 @@ svm_range_count_fault(struct amdgpu_device *adev, struct kfd_process *p,
 		WRITE_ONCE(pdd->faults, pdd->faults + 1);
 }
 
+/**
+ * svm_range_is_file_backed - decide if prange is file backed mmap
+ * @mm: the mm structure
+ * @prange: svm range structure
+ *
+ * Context: caller must hold mmap_read_lock
+ *
+ * Return:
+ * false if entire range is anonymous mapping
+ * true if entire or partial range is file backed, or invalid mapping address
+ */
+static bool
+svm_range_is_file_backed(struct mm_struct *mm, struct svm_range *prange)
+{
+	struct vm_area_struct *vma;
+	unsigned long start, end;
+
+	start = prange->start << PAGE_SHIFT;
+	end = (prange->last + 1) << PAGE_SHIFT;
+
+	do {
+		vma = find_vma(mm, start);
+		if (!vma || !vma_is_anonymous(vma))
+			return true;
+		start = min(end, vma->vm_end);
+	} while (start < end);
+
+	return false;
+}
+
 int
 svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 			uint64_t addr)
@@ -2496,6 +2526,10 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 		 svms, prange->start, prange->last, best_loc,
 		 prange->actual_loc);
 
+	/* for file backed range, use system memory pages for GPU mapping */
+	if (svm_range_is_file_backed(mm, prange))
+		goto out_validate_and_map;
+
 	if (prange->actual_loc != best_loc) {
 		if (best_loc) {
 			r = svm_migrate_to_vram(prange, best_loc, mm);
@@ -2520,6 +2554,7 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 		}
 	}
 
+out_validate_and_map:
 	r = svm_range_validate_and_map(mm, prange, gpuidx, false, false);
 	if (r)
 		pr_debug("failed %d to map svms 0x%p [0x%lx 0x%lx] to gpus\n",
@@ -2850,6 +2885,11 @@ svm_range_trigger_migration(struct mm_struct *mm, struct svm_range *prange,
 	int r = 0;
 
 	*migrated = false;
+
+	/* Don't migrate file backed range to VRAM */
+	if (svm_range_is_file_backed(mm, prange))
+		return 0;
+
 	best_loc = svm_range_best_prefetch_location(prange);
 
 	if (best_loc == KFD_IOCTL_SVM_LOCATION_UNDEFINED ||
-- 
2.17.1